The present invention relates to a device for determining coordinates of a point of an object in a reference system of coordinates and the orientation of the object in the space in a measuring position assumed by the object, said object being adapted to be moved from a start position having known coordinates and orientation to said measuring position, the device comprising means adapted to detect parameters associated with said movement and members adapted to calculate said coordinates and orientation of the object in the measuring position from information from the detecting means about said parameters and about the start position, and a method according to the preamble of the appended independent method claim.
The invention relates in particular, but not exclusively, to such devices used for programming of robots, such as welding robots or robots for spray application of paint, which for example xe2x80x9cworkxe2x80x9d with vehicle bodies. This particular field of use of such a device will hereinafter be described for illuminating the problem upon which the present invention is based.
The object of the device is usually constituted by a hand tool being moved by hand by a person between different positions along a work piece, such as a vehicle body, for storing the coordinates and the direction of a tool of the robot in these positions. The control unit for the robot interpolates successively the different positions stored for obtaining a movement of path of the tool of the robot.
Said known coordinates in one position, such as a start position, are usually obtained by the fact that one or more cameras are watching different optical points of the object placed in this position, and the real coordinates and orientation of the object in said start position are determined through the information so obtained from the camera or the cameras. However, it is sometimes necessary to move the object to parts along the path of movement of the tool of the robot, which are hidden by for example the object with which the robot shall xe2x80x9cworkxe2x80x9d, such as a vehicle body. This if for example the case with different positions being located inside or in any corner of the vehicle body. The object is in such cases moved as mentioned from the start position to the measuring position hidden at the same time as parameters associated with the movement are detected and said calculation of coordinates and orientation of the object in the measuring position may then be carried out from information from the detecting means about these parameters and about the start position.
Until now this has been made by using the robot itself for storing such positions and by measuring the rotation of the different robot arms about their axes. However, this is a very cumbersome and cost demanding way for calculating coordinates and orientation in said measuring position.
It is already known through for example DE 19626459-A1 and BE-1010211-A6 how an object may be moved in the way mentioned above for storing the movement of path of a robot between different positions.
The object of the present invention is to provide a device and a method of the type defined in the introduction, which enables a considerably easier determination of coordinates and orientation of a said measuring position than has been possible before.
This object is according to the invention obtained by the fact that in such a device said means comprise accelerometers arranged on the object and adapted to detect accelerations and retardations of the object during said movement, and that the calculating member is adapted to calculate said coordinates and orientation of the object in the measuring position on the basis of information from the accelerometers.
The coordinates and the orientation of the object in said measuring position may hereby be determined with a high accuracy through very simple means.
According to a preferred embodiment of the invention said means comprise six accelerometers, three adapted to detect acceleration and retardation for rotation in three planes being orthogonal with respect to each other and three adapted for detection of acceleration and retardation of the object in the direction of the perpendicular to one of said planes each. By arranging six such accelerometers all the components of the movement of the object at the movement between the start position and the measuring position may be reliably detected.
According to another preferred embodiment of the invention the object is intended to be moved from said measuring position to a third position having known coordinates and orientation of the object, the accelerometers are adapted to detect accelerations and retardations during this movement, the calculating member is adapted to calculate the coordinates and the orientation of the object in said third position from information from the accelerometers, a member is adapted to compare the values of the coordinates and orientation so calculated with the real ones, and the calculating member is adapted to calculate new coordinates and orientation for the object in said measuring position from the acceleration and retardation data detected during the first movement possibly corrected in accordance with deviations of coordinates and orientation established at said comparison. It is through this comparison possible to increase the accuracy further when determining the coordinates and the orientation of the object in said measuring position, thanks to the compensating for possible errors in the measuring of the accelerometers made possible here.
According to another preferred embodiment of the invention the device comprises a member adapted to measure the time needed for the movement of the object between the start position and the measuring position and between the measuring position and the third position and the calculating member is adapted to carry out an application of a weight factor on the correction as a consequence of said deviations depending upon the relations between the times needed for the two movements. The compensation may in this way get even better and the reliability of the values calculated for the coordinates and the orientation in the measuring position may be increased further.
According to another preferred embodiment of the invention the object is adapted to be moved between different positions along a path of movement desired for a part of a robot for storing coordinates and orientation of said part of the robot in these positions. A movement of path for a robot may by this be stored in a rapid and efficient way and with a high accuracy also for positions not allowing optical registration of the position of such an object. It is then advantageous that the calculating member is adapted to calculate coordinates for a centre point of a tool of a robot in said measuring position, in which this centre point for example in the case of a robot for spray application of paint corresponds to the desired centre hit point for the paint beam of the nozzle. In the case of a robot for spot welding the measuring position corresponds to the desired position for the tip of the welding electrode of the robot.
Another preferred embodiment of the invention is exactly related to that said object is adapted to be moved to bear against an object, which a robot is intended to treat while assuming said measuring position, which makes it easy to rapidly and with accuracy obtain exactly the measuring position asked for.
According to another preferred embodiment of the invention one or more cameras are arranged to watch the object and members are arranged to calculate said known coordinates and orientation on the basis of information from the camera or the cameras, and said measuring position is located outside the field of view for said camera or cameras. The device according to the invention is in exactly such a case of particular use, i.e. when an optical determination of different positions of the object is to be carried out and some of these positions are hidden and by that do not allow any optical determination.
The invention also relates to methods for determining coordinates of the point of an object in a reference system of coordinates and the orientation of the object in the space in a measuring position assumed by the object according to the appended method claims.
The advantages of these methods appear with no doubt from the discussion above of the device according to the invention and the preferred embodiments thereof.
Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims.